The Bypass Angioplasty Revascularization Investigation (BARI) is a randomized international multicenter clinical trial that compares a strategy of initial percutaneous transluminal coronary angioplasty (PTCA) to that of initial coronary artery bypass graft (CABG) surgery for selected patients with multivessel coronary artery disease (CAD). The primary hypothesis tested is that a strategy of initial PTCA is no worse than one of initial CABG when assessed by mortality at 5 years. Other major endpoints include: myocardial infarction, need for repeat procedures and hospitalizations, symptomatic and function status, radionuclide ejection fraction, quality of life and economic impact. The trial began July, 1987. Investigators from 14 primary sites and 4 satellites randomized 1829 patients. In addition, 2013 patients who were eligible but not randomized and a random sample of 422 patients deemed ineligible based on their angiogram were recruited into a registry. Important subgroups include older adults (39%), women (27%), and African Americans (6%), the largest number of such patients in any revascularization trial. Central radiographic laboratory review confirmed 3-vessel disease in 41% of patients and 73% had 3 or more significant coronary lesions. The original protocol includes clinic visits, telephone contacts, rest and exercise electrocardiograms, and blood lipids over a period of five years. By July, 1993, the first patient will have been followed 5 years and the last patient followed 2 years. Current funding would allow 5-year follow- up for only 35% of the patients. For randomized and registry patients, we propose to complete and report 5- year results, including periprocedural outcome, and to extend limited follow-up to 10 years. We will use the same methods of data collection and management, and continue the same lines of communication among the clinical sites, central laboratories, the data coordinating center and the NHLBI that have served BARI successfully to this point. Clinical sites will rely on the excellent relationships established with patients and referring physicians. The rationale for extension is based on prior observations that the benefit of CABG is frequently lost after 5 years and thus conclusions based on 5 years of follow-up may differ substantially from those observed at 10 years. BARI is the largest and most comprehensive randomized trial of contemporary PTCA and CABG. As we enter the next century, results of BARI will have significant impact on the practice of medicine for patients with CAD and on national health care policy.